1. Field of the Invention
This invention relates generally to a method for creating scar collagen, and more particularly to a method for initiating the formation and healing of scar collagen or bony callus, and subsequently remodelling the scar collagen or bony callus.
2. Description of Related Art
The skin is composed of two basic elements, the epidermis and the underlying dermis. The underlying dermis provides the main structural support of the skin. The epidermis contains the epithelial cells and pigment forming cells called melanocytes. The dermis varies in thickness throughout the body. For instance, the skin is 25 times thicker on the back than on the eyelid.
The dermis is composed mainly of an extracellular protein called collagen. Collagen exists as a triple helix with three polypeptide chains that are connected with heat labile and heat stable chemical bonds. When collagen is heated, alterations in the physical properties of this protein occur at a characteristic temperature. This structural transition occurs at a specific shrinkage temperature.
The phenomenon of thermal shrinkage of collagen begins with a denaturization of the triple helix of the collagen molecule. Thermal energy severs the heat labile bonds that stabilize the triple stranded helix. As a result, the longitudinal axis of the molecule contracts. Partial denaturization of collagen tissue occurs in second degree burns and is typically applied as a standard thermal gradient that is hotter on the surface and cooler in the underlying dermis. In burn patients, partial denaturization of dermal collagen provides a tightening effect on the skin. By applying a reverse thermal gradient which cools the surface of the skin while heating the underlying collagen-containing layers, contraction of collagen in the absence of a second degree burn (and its inherent blistering and pigmentary irregularities) is possible. Because collagen is found in tendon, bone, cartilage and all other connective tissue throughout the body, reverse thermal gradient contraction of collagen can have many applications.
The selective induction of the basic wound healing process serves as the basis for the second major application of thermal shrinkage of collagen. In higher developed animal species, the wound healing response to injury involves an initial inflammatory process that subsequently leads to the deposition of scar tissue. The initial inflammatory response consists of the infiltration by white blood cells or leukocytes that dispose of cellular debris. Forty-eight hours later, proliferation of fibroblasts at the injured site occurs. These cells then produce scar collagen that functions as the main support structure of a healed wound. The deposition and subsequent remodeling of this nascent scar collagen provides the means to alter the consistency and geometry of soft tissue for both aesthetic and reconstructive purposes.
There exists an aesthetic need to contract skin without the scars, surgical risks or pigmentary side effects of commonly employed technique. These techniques include surgical resection of skin and the use of lasers and chemical peels to achieve a tighter, more youthful skin appearance. Understandably, many patients are hesitant to subject themselves to these procedures, even though an overall aesthetic improvement is likely.
Skin resection procedures are limited in their application due to inherent scars. With face-lift procedures, scars can be hidden around the contour of the ear, thus providing an acceptable trade-off between the surgical scar and the aesthetic improvement. Surgical resection of skin on the hips, thighs, arms, knees and legs, however, provides only a modest improvement with fairly unsightly scarring. In addition, patients must undergo a post-operative phase of healing that may be both painful and inconvenient. Other risk factors, such as bleeding and infection, may prolong healing.
Liposuction is effective at removing fat in some areas, however, it does not tighten the skin envelope. Skin resurfacing techniques that secondarily tighten excess skin (such as laser and chemical peels) employ a standard thermal gradient that requires burning off the superficial skin as a second degree burn. The thermal effects of collagen contraction in the deeper dermis occur, but require a painful healing phase due to the second degree burn. These modalities depend upon reepithelialization with cell migration from the skin appendages. This process of reepithelialization is similar to the healing of any thermal burn and is more likely to cause pigmentary irregularities due to the destruction of melanocytes in the epidermis.
Adipose tissue, more commonly known as fat, is formed of cells containing stored lipid. Adipose tissue is often subdivided into small loculations by connective collagen tissue serving as the fibrous septae.
There exists a need for subcutaneously contracting of collagen without surgical scarring or pigmentary side effects of more invasive techniques. There is a further need for subcutaneously inducing the formation and contraction of scar collagen in a selected tissue site while creating no deeper than a second degree burn on the surface of the selected tissue site.